Define the terms apical dominance.

 Apical dominance : It is the phenomenon in which apical bud of shoot suppresses the development of lateral buds into branches. It is induced by the plant hormone auxin. 
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Sometimes the fruits fall even before they are ripe. Give reasons.

Fall of fruits is due to formation of abscission layers in their stalk. The formation of this layer is controlled by hormones auxins present in leaves. Abscission layer is sometimes formed earlier leading to fruit fall even before they ripe. Artificially it is done by spraying hormones encouraging abscission.
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How are plant hormones used to suppress weeds ?


Synthetic auxins are used to get rid of dicot, such as Dandlions and thistles in areas reserved for monocots such as grain fields. A dicot responds to unnaturally high concentrations of auxins by growing rapidly and then die; whereas monocot, remains unaffected by the treatment.

 

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In what ways can you compare growth of living systems quantitatively?

Quantitative comparisons between the growth of living system can  be made in two ways :

(i) By measuring and comparing the total growth per unit time. This is called the absolute growth rate.

(ii) The growth of the given system per unit time expressed on a common basis, e.g., per unit initial parameter. This is called the relative growth rate.

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What structural changes do the cells undergo during differentiation as tracheary elements?


The cells undergo the following structural changes during the process of differentiation as tracheary elements. 

i. The cells lose their protoplasm to form tracheary elements. 

ii. They also develop a very strong, elastic,
lignocellulosic secondary cell walls, to carry water to long distances even under extreme tension. 

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